For example, a dps that subs evade tanking would not have more damage output than one who subs mp support, but they each would have situations they're more suited for. The evader would have a bit of flexibility by being less dependent on the tank's aggro, but the mp support would be well suited for magic focused parties. Also, because their sub's performance depends on their main's, they wouldn't be focused on using their sub to improve their main but instead on maximizing their main's performance so their sub is most effective.